In a manufacturing process of a semiconductor device or a flat panel display (FPD), plasma is often used in a processing (e.g., etching, deposition, oxidation, or sputtering) in order to perform a reaction satisfactorily at a relatively low temperature. Conventionally, in such a plasma process, plasma generated by a high frequency discharge in a MHz region, or plasma generated by a microwave discharge in a GHz region, has been widely used.
The plasma generated by a microwave discharge has an advantage of being able to generate high-density plasma having a low electron temperature at a low pressure. Particularly, since a planar microwave introduction window structure incorporating a slot antenna is adopted, large-diameter plasma may be efficiently generated. Further, since no magnetic field is required, the microwave discharge has an advantage of simplifying a plasma processing apparatus.
Even in a microwave plasma processing apparatus, in order to generate plasma required for a desired process, it is necessary to supply a predetermined processing gas into a vacuum chamber (processing chamber) in order to discharge the processing gas in the chamber. In general, a dielectric window for microwave introduction is attached to the ceiling of the chamber as a top plate. In a plasma generating space within the chamber, an electric field and a radiation power of the microwaves are the strongest in the vicinity of the inside of the dielectric window (top plate). Thus, the highest plasma generation efficiency is obtained by introducing a processing gas to the vicinity thereof. Therefore, a gas introduction mechanism is commonly used to introduce a processing gas from the ceiling into the chamber through a gas flow path penetrating the dielectric window.
Indeed, the dielectric window also serves as a propagation path of the microwaves, and a microwave electric field is widely distributed therein. Thus, when the processing gas is exposed to the microwave field in the gas flow path of the dielectric window, the processing gas may be discharged. When the processing gas is discharged in the gas flow path of the dielectric window, the microwave power may be unnecessarily consumed, and the conductance may be reduced due to the deposition of decomposed products of the processing gas onto the wall of the gas flow path. In the worst case, the dielectric window may be damaged by the discharge.
As a technique for suppressing such an abnormal discharge inside the dielectric window, there is a conventional technique in which a wall of gas flow path or a gas injecting unit is made of a conductor to electromagnetically shield a processing gas flowing through the gas flow path inside the dielectric window, from the microwave electric field. However, in this technique, the gas injecting unit of the conductor (metal) facing the plasma generating space may be sputtered by the attack of ions from the plasma, resulting in contamination. In addition, when the microwave electric field is electromagnetically shielded, a uniform plasma processing may be hindered. Therefore, a method of controlling the pressure in the gas injecting unit in a high region significantly deviating from a Paschen discharge region, without using a metal injector in the gas injecting unit of the dielectric window, has been suitably used.
Meanwhile, a silicon nitride (SiN) film has been conventionally widely used to protect the surface or the side of a device element on the workpiece such as, for example, a semiconductor wafer. A plasma CVD method by a microwave discharge has been known as a film formation method of the SiN film. For example, Patent Document 1 discloses a film formation method in which microwaves are introduced into a processing container by a flat antenna having a plurality of holes to generate plasma, and a SiN film is formed on a workpiece in accordance with a plasma CVD method. In the film formation method, trisilylamine (TSA) is exemplified as a part of raw materials used for the formation of the SiN film. Further, Patent Document 2 discloses a technique of forming a SiN film on a workpiece in accordance with a plasma DVD method, using silane (SiH4) for a film formation raw gas.